| 1. |
- Bousquet, J. Jean, et al.
(författare)
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Next-generation ARIA care pathways for rhinitis and asthma : a model for multimorbid chronic diseases
- 2019
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Ingår i: Clinical and Translational Allergy. - : BMC. - 2045-7022. ; 9
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Forskningsöversikt (refereegranskat)abstract
- Background: In all societies, the burden and cost of allergic and chronic respiratory diseases are increasing rapidly. Most economies are struggling to deliver modern health care effectively. There is a need to support the transformation of the health care system into integrated care with organizational health literacy.Main body: As an example for chronic disease care, MASK (Mobile Airways Sentinel NetworK), a new project of the ARIA (Allergic Rhinitis and its Impact on Asthma) initiative, and POLLAR (Impact of Air POLLution on Asthma and Rhinitis, EIT Health), in collaboration with professional and patient organizations in the field of allergy and airway diseases, are proposing real-life ICPs centred around the patient with rhinitis, and using mHealth to monitor environmental exposure. Three aspects of care pathways are being developed: (i) Patient participation, health literacy and self-care through technology-assisted "patient activation", (ii) Implementation of care pathways by pharmacists and (iii) Next-generation guidelines assessing the recommendations of GRADE guidelines in rhinitis and asthma using real-world evidence (RWE) obtained through mobile technology. The EU and global political agendas are of great importance in supporting the digital transformation of health and care, and MASK has been recognized by DG Sante as a Good Practice in the field of digitally-enabled, integrated, person-centred care.Conclusion: In 20 years, ARIA has considerably evolved from the first multimorbidity guideline in respiratory diseases to the digital transformation of health and care with a strong political involvement.
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| 2. |
- Ivanov, Sergey A., et al.
(författare)
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Crystal structure and antiferromagnetic spin ordering of LnFe(2/3)Mo(1/3)O(3) (Ln = Nd, Pr, Ce, La) perovskites
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 91:9
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Tidskriftsartikel (refereegranskat)abstract
- Stoichiometric polycrystalline samples of LnFe(2/3)Mo(1/3)O(3) (Ln = Nd, Pr, Ce, La) have been prepared by solid-state reaction and studied by means of x-ray and neutron powder diffraction as well as Mossbauer spectroscopy and magnetic measurements. All samples were found to be of single phase and to have Pnma symmetry with valence state +3 of Fe and Mo. It is demonstrated that the B-site cations of LnFe(2/3)Mo(1/3)O(3) in accord with LnFeO(3) order in a G-type antiferromagnetic structure with the magnetic moments aligned along the b axis. However, with significantly lower Neel temperatures than their LnFeO(3) parent compounds. The Fe-O-Fe bond lengths and bond angles and thus themagnitude of the antiferromagnetic superexchange interaction are found to systematically change with the ionic radius of Ln such that T-N increases with increasing radius. Only the CeFe2/3Mo1/3O3 compound experiences a low temperature spin reorientation from alignment along the b axis to the a axis.
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| 3. |
- Ivanov, Sergey A., et al.
(författare)
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New insights into the multiferroic properties of Mn3TeO6
- 2017
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Ingår i: Journal of Physics D. - : IOP PUBLISHING LTD. - 0022-3727 .- 1361-6463. ; 50:8
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Tidskriftsartikel (refereegranskat)abstract
- Mn3TeO6 has a trigonal corundum related structure (space group R (3) over bar), and orders in an incommensurate antiferromagnetic (AFM) structure at T-N approximate to 24 K. A weak ferroelectric order below T* similar to 21 K has recently been reported. In order to investigate possible structural changes below T-N leading to the observed dipole order, we have performed a detailed study of the crystal and magnetic structures of Mn3TeO6 using neutron powder diffraction (NPD) in the temperature range of 5-40 K. Complementary low-temperature second harmonic generation (SHG) measurements were performed in order to confirm the reported dipole order at T*. No change in the rhombohedral symmetry associated with a possible displacive phase transition at T* was observed in the long-range structural correlations, and it appears that Mn3TeO6 keeps the same incommensurately modulated magnetic spin structure with the propagation vector k = (0; 0; 0.43) in the whole temperature range from 5 to 24 K.
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| 4. |
- Ivanov, Sergey A., et al.
(författare)
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Perovskite solid solutions La0.75Bi0.25Fe1-xCrxO3 : Preparation, structural, and magnetic properties
- 2017
-
Ingår i: Journal of Solid State Chemistry. - : Elsevier. - 0022-4596 .- 1095-726X. ; 254, s. 166-177
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Tidskriftsartikel (refereegranskat)abstract
- Solid solutions of La0.75Bi0.25Fe1−xCrxO3 (x = 0.1, 0.25, 0.5, and 0.75) prepared by conventional solid state reaction have been studied by means of X-ray powder diffraction (XRPD), neutron powder diffraction (NPD) and magnetic measurements. The NPD and XRPD patterns indicate orthorhombic structure (space group Pnma) for all compositions in the whole temperature range investigated (4–900 K). The lattice parameters of La0.75Bi0.25Fe1−xCrxO3 were found to decrease with the Cr content. It was established that the Fe3+ and Cr3+ cations are randomly positioned at the B-site of the perovskite structure.All samples order antiferromagnetically below transition temperatures that decrease with increasing Cr content, from around 700 K for x = 0.1 to about 300 K for x = 0.75. The antiferromagnetic arrangement of the Fe3+/Cr3+ magnetic moments in the B-site is of G-type along the x-axis (Gx mode) with propagation vector k = (0,0,0) for all concentrations of Cr. Effects of the composition on several structural distortion parameters were investigated and an anomalous variation of the octahedral deformation with Cr content was found. Whilst the overall octahedral deformation varies irregularly with increasing Cr content, the octahedral tilting was found to decrease monotoneously.
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| 5. |
- Ivanov, Sergey A., et al.
(författare)
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Spin and dipole order in geometrically frustrated mixed-valence manganite Pb3Mn7O15
- 2016
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Ingår i: Journal of materials science. Materials in electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 27:12, s. 12562-12573
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Tidskriftsartikel (refereegranskat)abstract
- The structural, magnetic, and dielectric properties of Pb3Mn7O15 have been investigated using high-quality single crystals. Pb3Mn7O15 adopts a pseudo-hexagonal orthorhombic structure, with partially filled Kagom, layers connected by ribbons of edge-sharing MnO6 octahedra and intercalated Pb cations. There are 9 inequivalent sites in the structure for the Mn ions, which exist both as Mn3+ and Mn4+. Pb3Mn7O15 undergoes an antiferromagnetic transition below T-N similar to 67 K, with significant geometric frustration. Neutron powder diffraction on crushed single crystals allowed us to determine the low-temperature antiferromagnetic magnetic structure. We discuss the magnetic interaction pathways in the structure and possible interplay between the structural distortions imprinted by the lone-electron pair of Pb2+ cations and Mn3+/Mn4+ charge ordering.
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| 6. |
- Ivanov, Sergey A., et al.
(författare)
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Structural and magnetic properties of nickel antimony ferrospinels
- 2015
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Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 158, s. 127-137
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Tidskriftsartikel (refereegranskat)abstract
- Spinel-type compounds of Fe-Ni-Sb-O system were synthesized as polycrystalline powders. The crystal and magnetic properties were investigated using X-ray and neutron powder diffraction, Mossbauer and X-ray absorption spectroscopy and magnetization measurements. The samples crystallize in the cubic system, space group Fd - 3 m. The distribution of cations between octahedral and tetrahedral sites was refined from the diffraction data sets using constraints imposed by the magnetic, Mossbauer and EDS results and the ionic radii. The cation distribution and the temperature dependence of the lattice parameter (a) and the oxygen positional parameter (u) were obtained. A chemical formula close to Fe0.8Ni1.8Sb0.4O4 was determined, with Sb5+ cations occupying octahedral sites, and Fe3+ and Ni2+ occupying both tetrahedral and octahedral sites. Fe3+ mainly (85/15 ratio) occupy tetrahedral sites, and conversely Ni2+ mainly reside on octahedral ones. The magnetic unit cell is the same as the crystallographic one, having identical symmetry relations. The results indicate that the compounds have a collinear ferrimagnetic structure with antiferromagnetic coupling between the tetrahedral (A) and octahedral (B) sites. Uniquely, the temperature dependence of the net magnetization of this rare earth free ferrimagnet exhibits a compensation point.
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| 7. |
- Ivanov, Sergey, et al.
(författare)
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Cation ordering, ferrimagnetism and ferroelectric relaxor behavior in Pb(Fe1-xScx)(2/3)W1/3O3 solid solutions
- 2019
-
Ingår i: European Physical Journal B. - : SPRINGER. - 1434-6028 .- 1434-6036. ; 92:8
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Tidskriftsartikel (refereegranskat)abstract
- Ceramic samples of the multiferroic perovskite Pb(Fe1-xScx)(2/3)W1/3O3 with 0 <= x <= 0.4 have been synthesized using a conventional solid-state reaction method, and investigated experimentally and theoretically using first-principle calculations. Rietveld analyses of joint synchrotron X-ray and neutron diffraction patterns show the formation of a pure crystalline phase with cubic (Fm3(_)m) structure with partial ordering in the B-sites. The replacement of Fe by Sc leads to the increase of the cation order between the B and B '' sites. As the non-magnetic Sc3+ ions replace the magnetic Fe3+ cations, the antiferromagnetic state of PbFe2/3W1/3O3 is turned into a ferrimagnetic state reflecting the different magnitude of the magnetic moments on the B ' and B '' sites. The materials remain ferroelectric relaxors with increasing Sc content. Results from experiments on annealed and quenched samples show that the cooling rate after high temperature annealing controls the degree of cationic order in Pb(Fe1-xScx)(2/3)W1/3O3 and possibly also in the undoped PbFe2/3W1/3O3.
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| 8. |
- Tellgren, Roland, 1930-, et al.
(författare)
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Substitution mechanism and structural study of Ag-doped LiCu2O2
- 2017
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Ingår i: Solid State Sciences. - : ELSEVIER SCIENCE BV. - 1293-2558 .- 1873-3085. ; 70, s. 36-40
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Tidskriftsartikel (refereegranskat)abstract
- Plate-like stoichiometric crystals of Ag-doped LiCu2O2 have been grown by slowly cooling Li2CO3 center dot 4(1 - x)CuO center dot 4xAgNO(3) (0 <= x <= 0.5) melts. X-ray single crystal diffraction has shown that the crystals are isostructural with LiCu2O2 and contain around 5 at % Ag (relative to the Cu atoms). The addition of silver to lithium cuprate crystals significantly increases their electrical conductivity but has little effect on the temperature behavior of their magnetic moment. The possible substitution mechanism is determined which supports Ag+ <-> Cu+, rather than Ag+ <-> Li+ in the Ag-doped LiCu2O2 crystals.
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| 9. |
- Akhter, Shahida, et al.
(författare)
-
Glassy behavior of diluted Cu-Zn ferrites
- 2018
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : ELSEVIER SCIENCE BV. - 0304-8853 .- 1873-4766. ; 452, s. 261-265
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic behavior of Zn substituted Cu-Zn spinel ferrites having chemical formula Cu1-xZnxFe2O4 (x = 0.7, 0.8, 0.9 and 1.0) has been studied by SQUID magnetometry, by means of magnetic hysteresis, field-cooled (FC) and zero-field-cooled (ZFC) magnetization, memory effect and low field ac susceptibility measurements. These measurements suggest that the ferrimagnetic phase of the x <= 0.8 samples is gradually turned into a spin glass (x >= 0.9). The compound with x = 0.9 exhibits the typical dynamical behavior of spin glasses, with indication of aging, rejuvenation and memory effects. The evolution of the magnetic properties of Cu-Zn spinel ferrites with substitution of Zn for Cu is discussed.
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| 10. |
- Andersson, Mikael Svante, et al.
(författare)
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Effects of the individual particle relaxation time on superspin glass dynamics
- 2016
-
Ingår i: PHYSICAL REVIEW B. - 2469-9950. ; 93:5
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Tidskriftsartikel (refereegranskat)abstract
- The low temperature dynamic magnetic properties of two dense magnetic nanoparticle assemblies with similar superspin glass transition temperatures T-g similar to 140 K are compared. The two samples are made from batches of 6 and 8 nm monodisperse gamma-Fe2O3 nanoparticles, respectively. The properties of the individual particles are extracted from measurements on reference samples where the particles have been covered with a thick silica coating. The blocking temperatures of these dilute assemblies are found at 12.5 K for the 6 nm particles and at 35 K for the 8 nm particles, which implies different anisotropy energy barriers of the individual particles and vastly different temperature evolution of their relaxation times. The results of the measurements on the concentrated particle assemblies suggest a strong influence of the particle energy barrier on the details of the aging dynamics, memory behavior, and apparent superspin dimensionality of the particles.
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| 11. |
- Andersson, Mikael Svante
(författare)
-
Interacting Magnetic Nanosystems : An Experimental Study Of Superspin Glasses
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents experimental results on strongly interacting γ-Fe2O3 magnetic nanoparticles and their collective properties. The main findings are that very dense randomly packed (≈60%) γ-Fe2O3 nanoparticles form a replica of a spin glass. The magnetic properties of the nanoparticle system are in most regards the same as those of an atomic spin glass. The system is therefore proposed as a model superspin glass. In superspin glasses the interacting building blocks that form the collective state are single domain nanoparticles, superspins with a magnetic moment of about 10000 μB, which can be compared to the atomic magnetic moment in spin glasses of approximately 1 μB. It was found that the relaxation time of the individual nanoparticles impacts the collective properties and governs the superspin dimensionality. Several dense compacts, each prepared with nanoparticles of a specific size, with diameters 6, 8, 9 and 11.5 nm, were studied. All the studied compacts were found to form a superspin glass state. Non-interacting reference samples, consisting of the same particles but coated with a silica shell, were synthesized to determine the single particle magnetic properties. It was also found that the effects of the nanoparticle size distribution, which lead to a variation of the magnetic properties, can be mitigated by having strong enough interparticle interactions. The majority of the work was carried out using SQUID magnetometry.
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| 12. |
- Andersson, Mikael Svante, et al.
(författare)
-
Magnetic properties of nanoparticle compacts with controlled broadening of the particle size distribution
- 2017
-
Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 95:18
-
Tidskriftsartikel (refereegranskat)abstract
- Binary random compacts with different proportions of small (volume V) and large (volume 2V) essentially bare maghemite nanoparticles are used to investigate the effect of controllably broadening the particle size distribution on the magnetic properties of magnetic nanoparticle assemblies with strong dipolar interaction. A series of eight random mixtures of highly uniform 9.0- and 11.5-nm-diameter maghemite particles prepared by thermal decomposition is studied. In spite of the severely broadened size distributions in the mixed samples, well-defined superspin glass transition temperatures are observed across the series, their values increasing linearly with the weight fraction of large particles.
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| 13. |
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| 14. |
- Andersson, Mikael Svante, et al.
(författare)
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Particle size-dependent superspin glass behavior in random compacts of monodisperse maghemite nanoparticles
- 2016
-
Ingår i: Materials Research Express. - : IOP Publishing. - 2053-1591. ; 3:4
-
Tidskriftsartikel (refereegranskat)abstract
- Dense random assemblies made from highly monodisperse gamma-Fe2O3 nanoparticles with sizes ranging from 6.2 to 11.5 nm have been investigated by DC and AC magnetometry. It is found that all assemblies undergo superspin glass phase transitions. The superspin glass phase transition temperature is strongly dependent on the particle size and the nature of the interparticle interaction. However the transition from superparamagnet to superspin glass, as evidenced by the shape of the ac-susceptibility curves and the dynamic critical exponents associated with the transition, is similar in all systems.
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| 15. |
- Andersson, Mikael Svante, et al.
(författare)
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Size-dependent surface effects in maghemite nanoparticles and its impact on interparticle interactions in dense assemblies
- 2015
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 26:47
-
Tidskriftsartikel (refereegranskat)abstract
- The question of the dominant interparticle magnetic interaction type in random closely packed assemblies of different diameter (6.2-11.5 nm) bare maghemite nanoparticles (NPs) is addressed. Single-particle magnetic properties such as particle anisotropy and exchange bias field are first of all studied in dilute (reference) systems of these same NPs, where interparticle interactions are neglible. Substantial surface spin disorder is revealed in all particles except the smallest, viz. for diameters d = 8-11.5 nm but not for d = 6.2-6.3 nm. X-ray diffraction analysis points to a crystallographic origin of this effect. The study of closely packed assemblies of the d >= 8 nm particles observes collective (superspin) freezing that clearly appears to be governed by interparticle dipole interactions. However, the dense assemblies of the smallest particles exhibit freezing temperatures that are higher than expected from a simple (dipole) extrapolation of the corresponding temperatures found in the d >= 8 nm assemblies. It is suggested that the nature of the dominant interparticle interaction in these smaller particle assemblies is superexchange, whereby the lack of significant surface spin disorder allows this mechanism to become important at the level of interacting superspins.
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| 16. |
- Andersson, Mikael S., et al.
(författare)
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Thermally induced magnetic relaxation in square artificial spin ice
- 2016
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of natural and artificial assemblies of interacting elements, ranging from Quarks to Galaxies, are at the heart of Physics. The collective response and dynamics of such assemblies are dictated by the intrinsic dynamical properties of the building blocks, the nature of their interactions and topological constraints. Here we report on the relaxation dynamics of the magnetization of artificial assemblies of mesoscopic spins. In our model nano-magnetic system - square artificial spin ice - we are able to control the geometrical arrangement and interaction strength between the magnetically interacting building blocks by means of nano-lithography. Using time resolved magnetometry we show that the relaxation process can be described using the Kohlrausch law and that the extracted temperature dependent relaxation times of the assemblies follow the Vogel-Fulcher law. The results provide insight into the relaxation dynamics of mesoscopic nano-magnetic model systems, with adjustable energy and time scales, and demonstrates that these can serve as an ideal playground for the studies of collective dynamics and relaxations.
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| 17. |
- Beran, P., et al.
(författare)
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Neutron powder diffraction study of Ba3ZnRu2-xIrxO9 (x=0, 1, 2) with 6H-type perovskite structure
- 2015
-
Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 50, s. 58-64
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Tidskriftsartikel (refereegranskat)abstract
- The triple perovskites Ba3ZnRu2-xIrxO9 with x = 0, 1, and 2 are insulating compounds in which Ru(Ir) cations form a dimer state. Polycrystalline samples of these materials were studied using neutron powder diffraction (NPD) at 10 and 295 K. No structural transition nor evidence of long range magnetic order was observed within the investigated temperature range. The results from structural refinements of the NPD data and its polyhedral analysis are presented, and discussed as a function of Ru/Ir content.
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| 18. |
- Cedervall, Johan, et al.
(författare)
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On the structural and magnetic properties of the double perovskite Nd2NiMnO6Nd2NiMnO6
- 2019
-
Ingår i: Journal of Materials Science: Materials in Electronics. - : Springer Science and Business Media LLC. - 1573-482X .- 0957-4522. ; 30:17, s. 16571-16578
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Tidskriftsartikel (refereegranskat)abstract
- The structural, electronic and magnetic properties of phase pure and stoichiometric samples of the double perovskite Nd 2NiMnO 6 have been investigated with a combination of X-ray and neutron diffraction, X-ray photoelectron spectroscopy and magnetometry. It is found that the monoclinic space group P2 1/ n best describes the crystal structure of Nd 2NiMnO 6. Photoectron spectroscopy revels a mixed valence of the transition metal sites where Ni has 3+/2+ oxidation states and Mn has 3+/4+. The compound orders ferromagnetically at ∼195 K. The magnetic structure was determined from the refinement of the neutron diffraction data. The results suggests that the B-site magnetic moments align along the crystallographic a-direction.
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| 19. |
- De Toro, José A., et al.
(författare)
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Remanence Plots as a Probe of Spin Disorder in Magnetic Nanoparticles
- 2017
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Ingår i: Chemistry of Materials. - Washington, D.C., USA : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 29:19, s. 8258-8268
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Tidskriftsartikel (refereegranskat)abstract
- Remanence magnetization plots (e.g., Henkel or delta M plots) have been extensively used as a straightforward way to determine the presence and intensity of dipolar and exchange interactions in assemblies of magnetic nanoparticles or single domain grains. Their evaluation is particularly important in functional materials whose performance is strongly affected by the intensity of interparticle interactions, such as patterned recording media and nanostructured permanent magnets, as well as in applications such as hyperthermia and magnetic resonance imaging. Here, we demonstrate that delta M plots may be misleading when the nanoparticles do not have a homogeneous internal magnetic configuration. Substantial dips in the delta M plots of gamma-Fe2O3 nanoparticles isolated by thick SiO2 shells indicate the presence of demagnetizing interactions, usually identified as dipolar interactions. results, however, demonstrate that it is the inhomogeneous spin structure of the nanoparticles, as most clearly evidenced by Mossbauer measurements, that has a pronounced effect on the delta M plots, leading to features remarkably similar to those produced by dipolar interactions. X-ray diffraction results combined with magnetic characterization indicate that this inhomogeneity is due to the presence of surface structural (and spin) disorder. Monte Carlo simulations unambiguously corroborate the critical role of the internal magnetic structure in the delta M plots. Our findings constitute a cautionary tale on the widespread use of remanence plots to assess interparticle interactions as well as offer new perspectives in the use of Henkel and delta M plots to quantify the rather elusive inhomogeneous magnetization states in nanoparticles.
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| 20. |
- Hudl, Matthias, et al.
(författare)
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PPMS-based set-up for Raman and luminescence spectroscopy at high magnetic field, high pressure and low temperature
- 2015
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Ingår i: EPJ Techniques and Instrumentation. - : Springer Science and Business Media LLC. - 2195-7045. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental set-up permitting Raman and luminescence spectroscopy studies in a commercial Physical Properties Measurement System (PPMS) from Quantum Design. Using this experimental set-up, gaseous, liquid and solid materials, in bulk or thin film form, may be investigated. The set-up is particularly suitable for the study of the spin-lattice coupling in strongly correlated oxide materials utilizing several different stimuli, e.g. magnetic and electric fields, high pressure and low temperatures. Details for the Raman extension, sample holder assembly and optical design, as well as data acquisition and measurement routine are described. Finally, we present exemplary results collected using the set-up, measured on reference materials, as well as on a correlated transition metal oxide.
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| 21. |
- Hudl, Matthias, et al.
(författare)
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Tunable exchange bias in dilute magnetic alloys - chiral spin glasses
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- A unidirectional anisotropy appears in field cooled samples of dilute magnetic alloys at temperatures well below the cusp temperature of the zero field cooled magnetization curve. Magnetization measurements on a Cu(13.5 at% Mn) sample show that this anisotropy is essentially temperature independent and acts on a temperature dependent excess magnetization, Delta M. The anisotropy can be partially or fully transferred from being locked to the direction of the cooling field at lower fields to becoming locked to the direction of Delta M at larger fields, thus instead appearing as a uniaxial anisotropy. This introduces a deceiving division of the anisotropy into a superposition of a unidirectional and a uniaxial part. This two faced nature of the anisotropy has been empirically scrutinized and concluded to originate from one and the same exchange mechanism: the Dzyaloshinsky-Moriya interaction.
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| 22. |
- Huyghe, Jeroen R., et al.
(författare)
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Discovery of common and rare genetic risk variants for colorectal cancer
- 2019
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Ingår i: Nature Genetics. - : Nature Publishing Group. - 1061-4036 .- 1546-1718. ; 51:1, s. 76-
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Tidskriftsartikel (refereegranskat)abstract
- To further dissect the genetic architecture of colorectal cancer (CRC), we performed whole-genome sequencing of 1,439 cases and 720 controls, imputed discovered sequence variants and Haplotype Reference Consortium panel variants into genome-wide association study data, and tested for association in 34,869 cases and 29,051 controls. Findings were followed up in an additional 23,262 cases and 38,296 controls. We discovered a strongly protective 0.3% frequency variant signal at CHD1. In a combined meta-analysis of 125,478 individuals, we identified 40 new independent signals at P < 5 x 10(-8), bringing the number of known independent signals for CRC to similar to 100. New signals implicate lower-frequency variants, Kruppel-like factors, Hedgehog signaling, Hippo-YAP signaling, long noncoding RNAs and somatic drivers, and support a role for immune function. Heritability analyses suggest that CRC risk is highly polygenic, and larger, more comprehensive studies enabling rare variant analysis will improve understanding of biology underlying this risk and influence personalized screening strategies and drug development.
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| 23. |
- Ivanov, Sergey A., et al.
(författare)
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Composition dependence of the multifunctional properties of Nd-doped Bi4Ti3O12 ceramics
- 2017
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Ingår i: Journal of materials science. Materials in electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 28:11, s. 7692-7707
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Tidskriftsartikel (refereegranskat)abstract
- Sample preparation, evolution of the crystal structure with Nd content at room temperature, as well as dielectric and magnetic properties of polycrystalline Bi4-xNdxTi3O12 solid solutions (x = 0.0, 0.5, 1.0, 1.5, and 2.0) are reported. These solid solutions were structurally characterized by X-ray powder diffraction using Rietveld refinements. For x <= 1.0, the samples crystallize in an orthorhombic symmetry. The structural data could be refined using the polar orthorhombic space group B2cb. The orthorhombicity decreases with increasing Nd3+ concentration, and a paraelectric tetragonal structure (space group I4/mmm) is stabilized for x > 1. The ferroelectric Curie temperature was found to monotonously decrease with increasing Nd concentration. A polar-to-nonpolar phase transition takes place near x = 1, reflecting the existence of a morphotropic phase boundary between 1.0 < x < 1.5 at room temperature. All samples were found to be paramagnetic down to 5 K, however, the presence of significant antiferromagnetic interaction is inferred from Curie-Weiss analyses of the temperature dependence of the magnetic susceptibility of the doped samples. The effect of Nd3+ substitution on structure-property relationship is discussed and compared to that of other lanthanide cations.
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| 24. |
- Ivanov, Sergey A., et al.
(författare)
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Evolution of the structural and multiferroic properties of PbFe2/3W1/3O3 ceramics upon Mn-doping
- 2017
-
Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 187, s. 218-232
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Tidskriftsartikel (refereegranskat)abstract
- The perovskite system Pb(Fe1-xMnx)(2/3)W1/3O3 (0 <= x <= 1, PFMWO) has been prepared by conventional solid-state reaction under different sintering conditions. Structures and phase composition as well as thermal, magnetic and dielectric properties of the compounds have been systematically investigated experimentally and by first-principles density functional calculations. A clean perovskite phase is established at room temperature for compositions 0 <= x <= 0.4. Rietveld refinements of X-ray and neutron powder diffraction patterns demonstrate that the compounds crystallize in space group Pm-3m (0 <= x <= 0.4). The degree of ordering of the Fe and W/Mn cations was found to depend on the concentration of Mn. First-principles calculations suggest that the structural properties of PFMWO are strongly influenced by the Jahn Teller effect. The PFMWO compounds behave as relaxor ferroelectrics at weak Mn-doping with a dielectric constant that rapidly decreases with increasing Mn content. A low temperature antiferromagnetic G-type order with propagation vector k = (1/2,1/2,1/2) is derived from neutron powder diffraction data for the samples with x <= 0.4. However with increasing doping concentration, the magnetic order is perturbed. First principles calculations show that the dominant exchange coupling is antiferromagnetic and occurs between nearest neighbor Fe atoms. When the system is doped with Mn, a relatively weak ferromagnetic (FM) interaction between Fe and Mn atoms emerges. However, due to the presence of this FM interaction, the correlation length of the magnetic order is greatly shortened already at rather low doping levels.
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| 25. |
- Ivanov, Sergey A, et al.
(författare)
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Polar Order and Frustrated Antiferromagnetism in Perovskite Pb2MnWO6 Single Crystals.
- 2016
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 55:6, s. 2791-2805
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Tidskriftsartikel (refereegranskat)abstract
- Single crystals of the multiferroic double-perovskite Pb2MnWO6 have been synthesized and their structural, thermal, magnetic and dielectric properties studied in detail. Pure perovskite-phase formation and stoichiometric chemical composition of the as-grown crystals are confirmed by X-ray single-crystal and powder diffraction techniques as well as energy-dispersive X-ray and inductively coupled plasma mass spectrometry. Detailed structural analyses reveal that the crystals experience a structural phase transition from the cubic space group (s.g.) Fm3̅m to an orthorhombic structure in s.g. Pn21a at about 460 K. Dielectric data suggest that a ferrielectric phase transition takes place at that same temperature, in contrast to earlier results on polycrystalline samples, which reported a transition to s.g. Pnma and an antiferroelectric low-temperature phase. Magnetic susceptibility measurements indicate that a frustrated antiferromagnetic phase emerges below 8 K. Density functional theory based calculations confirm that the cationic order between Mn and W is favorable. The lowest total energy was found for an antiferromagnetically ordered state. However, analyses of the calculated exchange parameters revealed strongly competing antiferromagnetic interactions. The large distance between the magnetic atoms, together with magnetic frustration, is shown to be the main reason for the low value of the ordering temperature observed experimentally. We discuss the structure-property relationships in Pb2MnWO6 and compare these observations to reported results on related Pb2BWO6 perovskites with different B cations.
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| 26. |
- Ivanov, Sergey A., et al.
(författare)
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Structure and magnetism in hexagonal tungsten bronze metal oxides AM(1/3)W(8/3)O(9) (A-K, Rb, Cs; M-Cr, Fe)
- 2015
-
Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 40, s. 44-49
-
Tidskriftsartikel (refereegranskat)abstract
- The structure and magnetic properties of hexagonal tungsten bronzes AM(1/3)W(8/3)O(9) (A-K+, Rb+, Cs+; M- Cr3+, Fe3+) have been investigated. Pure ceramic samples were synthesized by solid-state reaction. The samples have been studied by X-ray powder diffraction in combination with magnetic measurements. The compounds crystallize in hexagonal space group P6(3)/mcm. The substitution of magnetic ions into the WO6 octahedra yields dilute antiferromagnetic Cr3+-O2--Cr3+(or Fe3+-O2--Fe3+) superexchange interaction causing the appearance of short-range magnetic order at low temperatures. The antiferromagnetic character of the interaction is supported by negative values of the derived Curie-Weiss temperatures, qCW. The magnitude of qCW is found to decrease with increasing ionic radius of the A cation.
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| 27. |
- Ivanov, Sergey, et al.
(författare)
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Modification of the structure and magnetic properties of ceramic La2CoMnO6 with Ru doping
- 2018
-
Ingår i: Journal of Alloys and Compounds. - : ELSEVIER SCIENCE SA. - 0925-8388 .- 1873-4669. ; 752, s. 420-430
-
Tidskriftsartikel (refereegranskat)abstract
- Effects of Ru doping on the structure and magnetic properties of La2CoMn1-xRuxO6 ceramics with different compositions (x = 0, 0.1, 0.2, 0.3, 0.5, 0.75, 1.0) have been investigated using a variety of complementary techniques (X-ray powder diffraction and photoelectron spectroscopy, electron microscopy, and magnetometry). Phase-pure polycrystalline samples were prepared by the conventional solid-state reaction method including high pressure (3000 kg/cm(2) ) treatment of the original mixture of reagents. X-ray diffraction analyses of the samples accompanied with Rietveld refinement suggested a change in the crystal structure upon doping: for 0 <= x <= 0.3 the structure of the samples is predominantly disordered orthorhombic (s.g. Pnma) which transformed to ordered monoclinic (s.g. P2(1)/n) for 0.5 <= x <= 1. This suggests that Ru doping induces (partial) cation order in the B-sublattice. Magnetic measurements indicated a low temperature ferromagnetic phase, and a positive value of the Curie-Weiss temperature (theta cw) was derived for all samples of composition x <= 0.75. However, the Curie temperature (T-c) and theta cw decreased with increasing Ru doping. These changes in Tc upon doping can be correlated to the changes in the nearest neighbor and next nearest neighbor exchange interactions. The sample with x =1 orders antiferromagnetically at approximately 25 K.
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| 28. |
- Ivanov, Sergey, et al.
(författare)
-
Temperature-dependent structural and magnetic properties of R2MMnO6 double perovskites (R=Dy, Gd; M=Ni, Co)
- 2018
-
Ingår i: Journal of Materials Science: Materials in Electronics. - : Springer Science and Business Media LLC. - 1573-482X .- 0957-4522. ; 29:21, s. 18581-18592
-
Tidskriftsartikel (refereegranskat)abstract
- The structural and magnetic properties of the Dy2CoMnO6, Dy2NiMnO6 and Gd2CoMnO6 double perovskites are investigated using X-ray powder diffraction and squid magnetometry. The materials adopt an orthorhombic structure (space ground Pnma) with disordered Co(Ni)/Mn cations, and exhibit ferrimagnetic transitions near T(C)85, 95, and 115K respectively. T-C was found to monotonously depend on the orthorhombic distortion (a-c)/(a+c) of the compounds. The crystal structure of the compounds was investigated as a function of temperature (16-1100K range), evidencing changes in the BO6 octahedron near T-C. The magnetic entropy changes are estimated for comparison of the magnetocaloric properties to those from literature.
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| 29. |
- Joshi, Deep C., et al.
(författare)
-
Ferromagnetic excess moments and apparent exchange bias in FeF2 single crystals
- 2019
-
Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- The anisotropic antiferromagnet FeF2 has been extensively used as an antiferromagnetic layer to induce exchange bias effects in ferromagnetic/antiferromagnetic bilayers and heterostructures. In this work, an apparent exchange bias occurring in the low temperature hysteresis loops of FeF2 single crystals is investigated. A detailed investigation of the hysteresis and remnant magnetization indicates that the observation of an apparent exchange bias in FeF2 stems from an intrinsic excess moment associated with a distortion of the antiferromagnetic structure of piezomagnetic origin.
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| 30. |
- Joshi, Deep C., et al.
(författare)
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Room temperature ferrimagnetism in Yb-doped relaxor ferroelectric PbFe2/3W1/3O3
- 2019
-
Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 115:7
-
Tidskriftsartikel (refereegranskat)abstract
- We report ferrimagnetism and reentrant relaxor ferroelectricity near room temperature in a Yb-doped PbFe2/3W1/3O3 cubic perovskite. Structural analysis reveals the presence of a single cubic perovskite phase, with the m space group [lattice parameter: a=8.0112(3) angstrom], and partial B-site ordering. The B-site ordering yields uncompensated magnetic moments in the antiferromagnetic structure of PbFe2/3W1/3O3 and ferrimagnetism near room temperature. An excess moment of similar to 0.6 mu(B)/B-site may be estimated from magnetic hysteresis curves recorded up to 50kOe at 5K. The temperature dependent magnetodielectric study reveals a sequential phase transition from a long-range ferroelectric state (across 280K) to a short-range relaxor ferroelectric state (across 190K). The long-range ferroelectric ordering is found to be more affected by the application of external magnetic fields than the relaxor phase.
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| 31. |
- Kambhala, Nagaiah, et al.
(författare)
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Study of coexisting phases in Bi doped La0.67Sr0.33MnO3
- 2016
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 406, s. 22-29
-
Tidskriftsartikel (refereegranskat)abstract
- We report the remarkable phase separation behavior in La0.67Sr0.33MnO3 doped with Bi3+ ion at La site. The temperature dependent resistivity and magnetization of La0.67-xBixSr0.33MnO3 (x>0) show the presence of phase separation of ferromagnetic metallic and charge ordered antiferromagnetic insulating phases. Markedly, the field dependant magnetization studies of La0.67-xBixSr0.33MnO3 (x=0.3) show the metamagnetic nature of ferromagnetic metallic state implying the competition of coexisting ferromagnetic metallic and charge ordered antiferromagnetic phases. The electron spin resonance and exchange bias studies of La0.67-xBixSr0.33MnO3 (x=0.4 and 0.5) substantiate the coexistence of ferromagnetic clusters in antiferromagnetic matrix.
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| 32. |
- Kumar, Anil P., et al.
(författare)
-
Composition driven structural transition in La2-xSrxCuRuO6 (0 <= x <= 1) double perovskites
- 2017
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 693, s. 1096-1101
-
Tidskriftsartikel (refereegranskat)abstract
- We report results of detailed structural investigations on the system La2-xSrxCuRuO6 (0 <= x <= 1) as a function of composition using neutron powder diffraction. Our results reveal that this series of compounds exhibit an interesting structural transition manifested through Sr doping; with Ru in single valency, in end members, and mixed valency otherwise. The end members La2CuRuO6 and LaSrCuRuO6 crystallize in monoclinic structures with space group P2(1)/n. However, the compositions with intermediate Sr doping (x = 0.2 and 0.8) crystallize in triclinic structure with space group P-1, albeit with minute distortions. The detailed structural studies by neutron powder diffraction at room temperature and at 10 K, for compositions, x = 0.2, 0.8 and 1 are presented. While magnetic measurements are indicative of ferro and antiferromagnetic like transitions for x = 0 and x > 0 respectively, neutron diffraction patterns collected at 10 K and 30 K across the characteristic transition temperature suggested by the magnetic data, do not show any extra peaks or extra intensity at lower temperature as compared to the high temperature, thus, establishing the absence of any long-range magnetic ordering in these samples.
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| 33. |
- Liu, Lei, et al.
(författare)
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Bandgap engineering in Mn3TeO6 : giant irreversible bandgap reduction triggered by pressure
- 2019
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 55:80, s. 12000-12003
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the bandgap energy of the multiferroic oxide Mn3TeO6 is successfully reduced by similar to 39% from 3.15 eV to 1.86 eV, accompanied by a phase transition at high pressures. The high-pressure phase with smaller bandgap energy is quenchable to ambient conditions and represents a promising light-harvesting material for photovoltaic applications.
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| 34. |
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| 35. |
- Liu, Lei, et al.
(författare)
-
Bandgap engineering in Mn3TeO6: giant irreversible bandgap reduction triggered by pressure
- 2019
-
Ingår i: Chemical Communications. - 1359-7345 .- 1364-548X. ; 55, s. 12000-
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the bandgap energy of the multiferroic oxide Mn3TeO6 is successfully reduced by ∼39% from 3.15 eV to 1.86 eV, accompanied by a phase transition at high pressures. The high-pressure phase with smaller bandgap energy is quenchable to ambient conditions and represents a promising light-harvesting material for photovoltaic applications.
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| 36. |
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| 37. |
- Liu, Lei, et al.
(författare)
-
Pressure-induced polymorphism and piezochromism in Mn2FeSbO6
- 2019
-
Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 114:16
-
Tidskriftsartikel (refereegranskat)abstract
- In the last decade, major efforts have been devoted to searching for polar magnets due to their vast potential applications in spintronic devices. However, the polar magnets are rare because of conflicting electronic configuration requirements of ferromagnetism and electric polarization. Double-perovskite oxides with a polar structure containing transition metal elements represent excellent candidates for the polar magnet design. Herein, the crystal structure evolution of Mn2FeSbO6 (MFSO) was investigated at pressures reaching similar to 50 GPa by in situ synchrotron X-ray diffraction (XRD), Raman scattering, and ab initio calculation techniques. The XRD results reveal ilmenite-to perovskite-type phase transition at around 35 GPa. An additional intermediate phase, observed in the range of 31-36 GPa by Raman spectroscopy, but not the XRD technique, is proposed to represent the polar LiNbO3 phase. It is argued that this phase emerged due to the heating effect of the Raman-excitation laser. The LiNbO3-type MFSO compounds, displaying an intrinsic dipole ordering, represent a promising candidate for multiferroic materials. The detected phase transitions were found to be reversible although a significant hysteresis was noticeable between compression and decompression runs. Moreover, a pressure-induced piezochromism, signifying a bandgap change, was discovered by the direct visual observations and corroborated by ab initio calculations. The present study benefits an efficient high-pressure synthesis of polar magnetic double-perovskite oxides in the future.
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| 38. |
- Liu, Lei, et al.
(författare)
-
Pressure tuning of octahedral tilt in the ordered double perovskite Pb2CoTeO6
- 2019
-
Ingår i: Journal of Alloys and Compounds. - : ELSEVIER SCIENCE SA. - 0925-8388 .- 1873-4669. ; 801, s. 310-317
-
Tidskriftsartikel (refereegranskat)abstract
- Double perovskites represent a family of materials with promising fundamental properties (e.g. multiferroicity) and vast potential applications. However, the knowledge of pressure effects on the crystal structure of double perovskite is limited, which hinders their efficient synthesis using high-pressure techniques. Pb2CoTeO6 (PCTO) is considered as a good candidate for multiferroic materials, although a polymorph with a polar structure has not been synthesized yet. In the present study, the pressure effect on the crystal structure of PCTO was systematically studied by employing in situ synchrotron X-ray powder diffraction and Raman scattering techniques up to 60 GPa. A structural phase transition from R-3 to I2/m structure was observed at around 20 GPa, indicating that increasing the pressure has a similar effect on PCTO as decreasing the temperature, i.e., promoting the distortion of the structure. No polar structure of PCTO has been observed in the applied pressure range. The present study provides a valuable information about the crystal structure evolution of double perovskites upon compression, and will benefit high-pressure syntheses of novel double perovskites in the future.
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| 39. |
- Margaris, G., et al.
(författare)
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Superspin glass state in a diluted nanoparticle system stabilized by interparticle interactions mediated by an antiferromagnetic matrix
- 2017
-
Ingår i: Nanotechnology. - : IOP PUBLISHING LTD. - 0957-4484 .- 1361-6528. ; 28:3
-
Tidskriftsartikel (refereegranskat)abstract
- In nanoparticle systems consisting of two magnetic materials (bi-magnetic nanoparticles or nanoparticles embedded in a magnetic matrix), there is a constantly growing interest in the investigation of the interplay between interparticle interactions and the nanoparticle-matrix interface exchange coupling, because of its enormous impact on a number of technological applications. The understanding of the mechanisms of such interplay is a great challenge, as it would allow controlling equilibrium and non-equilibrium magnetization dynamics of exchange coupled nanoparticles systems and finely tuning their anisotropy. Here, we provide evidence that this interplay leads to a collective superspin glass (SSG) behavior in a system of diluted ferromagnetic. (FM) nanoparticles embedded in an antiferromagnetic (AFM) matrix (5% volume fraction of Co particles in Mn film matrix). We have developed a novel mesoscopic model to study the influence of interparticle interaction on the exchange bias (EB) and the dynamical behavior of assemblies of FM nanoparticles embedded in a granular AFM matrix. Our mesoscopic model is based on reducing the amount of simulated spins to the minimum number necessary to describe the magnetic structure of the system and introducing the adequate exchange parameters between the different spins. The model replicates remarkably well the observed static and dynamical SSG properties as well as the EB behavior. In addition, the proposed model well explains the role of the significant Co/Mn alloying and of the granularity of the matrix in mediating interparticle interactions through exchange and dipole-dipole coupling between the uncompensated moments of its grains and the exchange interaction at the Co/Mn interface.
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| 40. |
- Monsen, Asmund, et al.
(författare)
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Point contact investigations of film and interface magnetoresistance of La0.7Sr0.3MnO3 heterostructures on Nb:SrTiO3
- 2015
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 374, s. 433-439
-
Tidskriftsartikel (refereegranskat)abstract
- STM based magnetotransport measurements of epitaxial La0.7Sr0.3MnO3 31 nm thick films with and without an internal LaMnO3 layer (0-3.1 nm thick) grown on Nb doped SrTiO3 are presented. The measurements reveal two types of low field magnetoresistance (LFMR) with a magnitude of similar to 0.1-1.5%. One LFMR contribution is identified as a conventional grain boundary/domain wall scattering through the symmetric I-V characteristics, high dependence on tip placements and insensitivity to introduction of LaMnO3 layers. The other contribution originates from the reverse biased Nb doped SrTiO3 interface and the interface layer of La0.7Sr0.3MnO3. Both LFMR contributions display a field dependence indicative of a higher coercivily (similar to 200 Oe) than the bulk film. LaMnO3 layers are found to reduce the rectifying properties of the junctions, and sub micron lateral patterning by electron beam lithography enhances the dioclic properties, in accordance with a proposed transport model based on the locality of the injected current.
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| 41. |
- Muscas, Giuseppe, et al.
(författare)
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Designing new ferrite/manganite nanocomposites
- 2016
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 8:4, s. 2081-2089
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Tidskriftsartikel (refereegranskat)abstract
- Two kinds of nanocomposites of transition metal oxides were synthesized and investigated. Each nanocomposite comprises nanoparticles of La0.67Ca0.33MnO3 and CoFe2O4 in similar volume fractions, however arranged with different morphologies. The temperature-dependent magnetic and electrical properties of the two systems are found to greatly differ, suggesting different degrees of interaction and coupling of their constituents. This is confirmed by magnetic field-dependent experiments, which reveal contrasted magnetization reversal and magnetoresistance in the systems. We discuss this morphology-physical property relationship, and the possibility to further tune the magnetism and magneto-transport in such nanocomposites.
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| 42. |
- Muscas, Giuseppe, et al.
(författare)
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The interplay between single particle anisotropy and interparticle interactions in ensembles of magnetic nanoparticles
- 2018
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 20, s. 28634-28643
-
Tidskriftsartikel (refereegranskat)abstract
- This paper aims to analyze the competition of single particle anisotropy and interparticle interactions in nanoparticle ensembles using a random anisotropy model. The model is first applied to ideal systems of non-interacting and strongly dipolar interacting ensembles of maghemite nanoparticles. The investigation is then extended to more complex systems of pure cobalt ferrite CoFe2O4 (CFO) and mixed cobalt-nickel ferrite (Co,Ni)Fe2O4 (CNFO) nanoparticles. Both samples were synthetized by the polyol process and exhibit the same particle size (D-TEM approximate to 5 nm), but with different interparticle interaction strengths and single particle anisotropy. The implementation of the random anisotropy model allows investigation of the influence of single particle anisotropy and interparticle interactions, and sheds light on their complex interplay as well as on their individual contribution. This analysis is of fundamental importance in order to understand the physics of these systems and to develop technological applications based on concentrated magnetic nanoparticles, where single and collective behaviors coexist.
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| 43. |
- Muscas, Giuseppe, et al.
(författare)
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Tuning the Size and Shape of Oxide Nanoparticles by Controlling Oxygen Content in the Reaction Environment : Morphological Analysis by Aspect Maps
- 2015
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 27:6, s. 1982-1990
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Tidskriftsartikel (refereegranskat)abstract
- The thermal decomposition of acetylacetonate precursors is one of the most employed syntheses to prepare high quality colloidal magnetic nanopartides. In this paper, an advanced version of this synthetic approach was developed to prepare cobalt ferrite nanopartides, introducing for the first time a rigorous control on one commonly neglected reaction parameter, that is, the residual oxygen content in the reaction environment. A new concept derived from the statistical analysis of S(T)EM images, i.e., the so-called aspects maps, was introduced: this tool has allowed us to clearly identify the optimal value of pressure to produce particles with an average size,similar to 19 nm and with a very narrow size distribution (polydispersity 0.4 nm(-1)). The magnetic properties of this sample were also analyzed, and a strong improvement of the magnetization reversal mechanism, which is a critical issue for several technological applications, was observed.
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| 44. |
- Nag, Abhishek, et al.
(författare)
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Ba3MIr2O9 hexagonal perovskites in the light of spin-orbit coupling and local structural distortions
- 2018
-
Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 97:6
-
Tidskriftsartikel (refereegranskat)abstract
- Spin-orbit coupling (SOC) is found to be crucial for understanding themagnetic and electronic properties of 5d transitionmetal oxides. In 5d systems, with Ir5+ ions, where ideally a nonmagnetic J = 0 ground state is expected to be stabilized in the presence of strong SOC, often spontaneous moments are generated due to hopping induced superexchange. This effect is more pronounced when the Ir atoms are close by, as in systems with Ir2O9 dimers in 6H Ba3MIr2O9 compounds where magnetism is an outcome of complex Ir-O-Ir exchange paths, and is strongly influenced by the presence of local distortions. We find that subtle variations in the local structure of Ba3MIr2O9 (M = Mg, Sr, and Ca) lead to markedly differentmagnetic properties. While SOC plays a pivotal role in explaining the insulating ground states of these systems, it is seen that Ba3MgIr2O9, having a P6(3)/mmc symmetry, does not order down to low temperature despite having antiferromagnetic exchange interactions, while Ba3CaIr2O9 shows weak dimer-like features and stabilizes in C2/c' magnetic configuration with no net moment, and Ba3SrIr2O9 possesses a ground state corresponding to themagnetic space groupC2'/c' and exhibits ferromagnet-like features.
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| 45. |
- Nag, Abhishek, et al.
(författare)
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Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba3ZnIr2O9
- 2016
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 116:9
-
Tidskriftsartikel (refereegranskat)abstract
- We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d(4)) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J = 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK.
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| 46. |
- Nayak, S., et al.
(författare)
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Magnetic compensation, field-dependent magnetization reversal, and complex magnetic ordering in Co2TiO4
- 2015
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:21
-
Tidskriftsartikel (refereegranskat)abstract
- The complex nature of magnetic ordering in the spinel Co2TiO4 is investigated by analyzing the temperature and magnetic field dependence of its magnetization (M), specific heat (C-p), and ac magnetic susceptibilities chi' and chi ''. X-ray diffraction of the sample synthesized by the solid-state reaction route confirmed the spinel structure whereas x-ray photoelectron spectroscopy shows its electronic structure to be Co2TiO4 = [Co2+][Co3+ Ti3+]O-4. From analysis of the temperature dependence of the dc paramagnetic susceptibility, the magnetic moments mu(A) = 3.87 mu(B) and mu(B) = 5.19 mu B on the A and B sites are determined with mu(B) in turn yielding mu(Ti3+) = 1.73 mu(B) and mu(Co3+) = 4.89 mu(B). Analysis of the dc and ac susceptibilities combined with the weak anomalies observed in the C-p vs T data shows the existence of a quasi-long-range ferrimagnetic state below T-N similar to 47.8K and a compensation temperature T-comp similar to 32 K, the latter characterized by sign reversal of magnetization with its magnitude depending on the applied magnetic field and the cooling protocol. Analysis of the temperature dependence of M (field cooled) and M (zero field cooled) data and the hysteresis loop parameters is interpreted in terms of large spin clusters. These results in Co2TiO4, significantly different from those reported recently in isostructural Co2SnO4 = [Co2+][Co2+ Sn4+]O-4, warrant further investigations of its magnetic structure using neutron diffraction.
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| 47. |
- Normile, P. S., et al.
(författare)
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Demagnetization effects in dense nanoparticle assemblies
- 2016
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 109:15
-
Tidskriftsartikel (refereegranskat)abstract
- We highlight the relevance of demagnetizing-field corrections in the characterization of dense magnetic nanoparticle assemblies. By an analysis that employs in-plane and out-of-plane magnetometry on cylindrical assemblies, we demonstrate the suitability of a simple analytical formula-based correction method. This allows us to identify artifacts of the demagnetizing field in temperature-dependent susceptibility curves (e.g., shoulder peaks in curves from a disordered assembly of essentially bare magnetic nanoparticles). The same analysis approach is shown to be a straightforward procedure for determining the magnetic nanoparticle packing fraction in dense, disordered assemblies.
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| 48. |
- Padam, R., et al.
(författare)
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Magnetic phase diagram of Co(Cr1-xAlx)2O-4 (x=0.0-1.0)
- 2017
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 122:7
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Tidskriftsartikel (refereegranskat)abstract
- We report the role of Al substitution in the magnetic properties of spinel CoCr2O4 by means of temperature dependent dc and ac magnetization and heat capacity measurements. Various compositions (0.0 <= x <= 1.0) of polycrystalline Co(Cr1-xAlx)(2)O-4 samples have been prepared by sol-gel processing and their crystal structure was investigated by X-ray diffraction which was found to crystallize in the normal cubic spinel structure. For x <= 0.1, the system exhibits multiple magnetic orderings (long range ferrimagnetic ordering T-C, spin-spiral ordering T-S, and lock-in transition T-L), similar to that of the parent compound, CoCr2O4. However, all the compositions between x = 0.1 and 0.5 exhibit long range ferrimagnetic ordering below T-C and also a short range order at low temperature. Spin-glass like ordering was noticed between x = 0.6 and 0.8 due to the diluted B-site occupancy, whereas the end compound CoAl2O4 (x = 1.0) shows antiferromagnetic behavior. On the basis of these results, we propose a magnetic phase diagram for the Co(Cr1-xAlx)(2)O-4 series as a function of the Al content (x) and measuring temperature (T).
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| 49. |
- Pal, Somnath, et al.
(författare)
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Peculiar magnetic states in the double perovskite Nd2NiMnO6
- 2019
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 100:4
-
Tidskriftsartikel (refereegranskat)abstract
- We present magnetic measurements on Nd2NiMnO6 which exhibits a well-known insulating paramagnetic state to an insulating ferromagnetic state transition when cooled below 200 K. Beyond this basic fact, there is a great deal of diversity in the reported magnetic properties and interpretation of specific anomalies observed in the magnetic data of this compound below the Curie temperature. We address specifically two anomalies discussed in the past, namely, a spin-glass like behavior observed in some samples near 100 K and a downturn in the magnetization with a lowering of the temperature below approximately 50 K. We show for the first time that the application of an increasing magnetic field can systematically change the low-temperature behavior to make the down-turn in the magnetization into an upturn. With the help of first principle calculations and extensive simulations along with our experimental observations, we provide a microscopic understanding of all magnetic properties observed in this interesting system to point out that the glassiness around 100 K is absent in well-ordered samples and that the low-temperature magnetic anomaly below 50 K is a consequence of a ferromagnetic coupling of the Nd spin moments with the spin of the Ni-Mn ordered sublattice without giving rise to any ordering of the Nd sublattice that remains paramagnetic, contrary to earlier claims. We explain this counter-intuitive interpretation of a ferromagnetic coupling of Nd spins with Ni-Mn spin giving rise to a decrease in the total magnetic moment by noting the less than half-filled 4f occupation of Nd that ensures orbital and spin moments of Nd to be opposite to each other due to the spin-orbit coupling. Since the ground state total magnetic moment of Nd has a contribution from the orbital moment, that is larger than the spin moment, the total moment of Nd is indeed pointing in a direction opposite to the direction of spin moments of the Ni-Mn sublattice as a consequence of the ferromagnetic exchange coupling between Nd and Ni-Mn spins.
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| 50. |
- Peddis, D., et al.
(författare)
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Magnetic anisotropy and magnetization dynamics of Fe nanoparticles embedded in Cr and Ag matrices
- 2015
-
Ingår i: Philosophical Magazine. - : Informa UK Limited. - 1478-6435 .- 1478-6443. ; 95:33, s. 3798-3807
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Tidskriftsartikel (refereegranskat)abstract
- Static and dynamical magnetic properties of Fe nanoparticles (NPs) embedded in non-magnetic (Ag) and antiferromagnetic (Cr) matrices with a volume filling fraction (VFF) of 10% have been investigated. In both Fe@Ag and Fe@Cr nanocomposites, the Fe NPs have a narrow size distribution, with a mean particle diameter around 2nm. In both samples, the saturation magnetization reaches that of Fe bulk bcc, suggesting the absence of alloying with the matrices. The coercivity at 5K is much larger in Fe@Cr than in Fe@Ag as a result of the strong interaction between the Fe NPs and the Cr matrix. Temperature-dependent magnetization and ac-susceptibility measurements point out further evidence of the enhanced interparticle interaction in the Fe@Cr system. While the behaviour of Fe@Ag indicates the presence of weakly interacting magnetic monodomain particles with a wide distribution of blocking temperatures, Fe@Cr behaves like a superspin glass produced by the magnetic interactions between NPs.
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